This invention relates to a process for producing a protein or low-molecular weight peptide composition mainly based on dipeptides and tripeptides, and an oral or enteral nutrient agent comprising the thus produced low-molecular peptide composition.
Heretofore, particularly in the food industry, peptides and amino acids have been produced through enzymatic hydrolysis of protein material. However, such attempts have been limited to the enzymatic hydrolysis of protein material for solubilization thereof and the conversion of protein material to lower polymers (with a molecular weight of higher than several thousand) serviceable in a nutritional form. Attention has been paid to the attribute of proteolytic products, but not to their molecular weight as such.
Making researches on the digestion and absorption of the enzymatic hydrolysis product of protein material, the inventors have found that by (1) reducing the average molecular weight to 1,500 or lower, preferably 700 or lower, (2) reducing the content of those peptides having a molecular weight of 2,000 or higher, preferably 1,000 or higher to 20% by weight or less, and (3) reducing the content of free amino acids to 20% by weight or less, that is, by producing a low-molecular weight peptide composition mainly based on dipeptides and tripeptides, a number of advantages are obtained as described below.
(1) This low-molecular weight peptide composition is different in enteral absorption from protein materials or amino acid mixtures containing the same amino acid constituents. Total nitrogen absorption rate is increased and the absorption antagonism between amino acids is minimized.
(2) It is an efficient nitrogen source because of improved nitrogen balance.
(3) Weight gain is remarkably increased.
(4) Cholesterol value in blood is reduced.
Conventional peptized products have either a low degree of proteolysis or an extremely high content of free amino acids. Differently stated, because of varying degrees of proteolysis, they contain from those peptides having a molecular weight of several ten thousand to free amino acids. Some products have an average molecular weight of higher than several thousand and some contain more than 50% of free amino acids.
The inventors have found that when used as a nutrient agent, a peptide composition which is limited within a narrow range of molecular weight is more effective and efficient in digestion and absorption or in physiological alimentation than conventional products such as solubilized protein materials, peptide mixtures having a wide distribution of molecular weight, or amino acid mixtures. The low-molecular weight peptide composition to be included in a nutrient agent according to the present invention is mainly based on dipeptides and tripeptides and contains 20% by weight or less of peptides having a molecular weight of 700 or higher and 20% by weight or less of free amino acids, said composition being produced by controlling the molecular weight of protein raw material as specified above.
Recently, it is believed that dipeptides and tripeptides are readily absorbed enterally. The inventors have for the first time confirmed this fact by in vivo experiments for a mixture of these peptides as described in detail hereinafter.
The inventors have also found that although free amino acid mixtures tend to be unevenly absorbed due to antagonism or reduced solubility, low-molecular weight peptides are free of such uneven absorption. Accordingly, such low-molecular weight peptide compositions as described above are preferred as a protein source for a nutrient agent.
As no importance has been attached to the low-molecular weight peptides which have apparent utility as mentioned above, any effective process for the production thereof has not been developed. It is therefore, a primary object of the present invention to provide a process for producing a low-molecular weight peptide composition mainly based on dipeptides and tripeptides, that is, having an average molecular weight of about 400 and a free amino acid content of 20% by weight or less.
Another object of the present invention is to provide a process for producing a low-molecular peptide composition as specified above from a protein raw material from any suitable source in high yields.
A further object of the present invention is to provide a process for producing a low-molecular peptide composition in which amino acid absorption antagonism is minimized and the content of free amino acids is reduced.
It is a secondary object of the present invention to provide a nutrient agent comprising a low-molecular weight peptide composition mainly based on dipeptides and tripeptides which is an efficient nitrogen source at it has reduced amino acid absorption antagonism, increased solubility, increased total nitrogen absorption rate, and improved nitrogen balance.
It is a further object of the present invention to provide a low-molecular peptide containing nutrient agent which serves as an efficient nitrogen source capable of providing an positive weight gain and a reduced cholesterol value in blood.
It is a still further object of the present invention to provide a nutrient agent in which protein material is hydrolyzed into well-absorbable low-molecular peptides, typically dipeptides and tripeptides so that it can be administered not only as an oral nutrient agent capable of easy alimentation, but also as an enteral nutrient agent directly into the stomach of a weak patient.